The present invention relates to a battery power supply. More particularly, the present invention relates to a battery power supply capable of providing high current for limited periods of time to satisfy the power demands of loads that create such demands.
Many modern digital devices, such as digital cell telephones, require from a battery high total energy, periodic bursts of power, and moderate average power. Some of these devices require batteries which, at least part of the time, must supply current and power (xe2x80x9cpower pulsesxe2x80x9d) far in excess of the average current and power used in the device""s operating cycle. As the battery discharges, its internal resistance increases, and it becomes increasingly difficult for the battery to provide the required power pulses at an acceptable voltage. In some environments, such as low temperature environments, even a new battery has an insufficient operating voltage to supply the power pulses. For one example, this is particularly true of zinc-air batteries. The sluggish gas phase oxygen reduction reaction, with its high overvoltage at the air cathode, has a poorer pulse voltage response than conventional high-power, solid phase, positive electrodes such as nickel hydroxide and silver oxide.
With the increased use of digital systems, power pulses and the problems associated with them have multiplied. Digital systems vary in their power requirements; some require power spikes of 5 amps for 20 msec and 10 Hz, while others have narrower pulses with lower power/current requirements and frequencies in the 200 Hz range. The duty cycle for GSM (General Systems Mobile) in one particular cellular phone application has a pulse of approximately 0.5 msec, and a peak current of 1.42 amps, which must be supplied at 6 volts. It has an average current of 0.22 amps over a period of approximately 4.6 msec. The total duty cycle is about 5.1 msecs.
A battery power source employs a pulse battery with one of the electrodes of the pulse battery having at least two electroactive materials as components of the same electrode. These different electroactive materials are selected to have different discharge potentials, charging potentials, and voltage outputs. One of the materials provides a voltage output of a predetermined level and the other of the materials lowers the overall charging voltage of the electrode below that of the first material. Preferably, the second material is present in an amount of at least 5 weight percent. In an embodiment, the negative electrode has at least two electroactive materials as components of the same electrode. The materials may be selected from the group consisting of zinc, gallium, tin, cadmium, lead, indium, bismuth and metal hydrides.
The battery power source is particularly suited to application in a power supply in which an auxiliary pulse battery backs up a battery that supplies the high total energy and average power requirement. The auxiliary battery supplies power to satisfy the demands of circuits requiring pulsed energy discharges on the order of a few milliseconds.
A mixed electrode is a battery electrode with at least two electroactive independent materials in the same electrode. The mixed electrode in the pulse battery permits the pulse battery to charge during the off-pulse periods throughout a substantial portion of the entire discharge voltage range of a primary battery. Thus, the primary battery is not required to provide very tight voltage ranges over its discharge cycle or history during operation with a pulsatile load (characterized by a temporally non-uniform load). For example, the primary battery (or xe2x80x9cenergy batteryxe2x80x9d) may be a zinc-air battery. The primary battery should be sized and selected such that it supplies most of the energy when the two are connected in parallel.
With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.